Casting method



"United States Patent Q CASTING METHOD Warren Jackson, Jr., Lyi1dhurst,Ohio, assignor to The sagdhlard Oil Company, Cleveland, Ohio, incorporation 0 Application July 8, 1953, Serial No. 366,749

5 Claims. (Cl. 18-58) The present invention relatesto a novel method ofcasting solid material consisting of, at least, two components and tothe castings soproduced.

To the best of my knowledge the art relating to the casting of solidscontaining two or more components, e. g.,

metal alloys and mixtures of hydrocarbons that are solid at ordinarytemperatures, has been concerned primarily with the problems ofobtaining castings that are uniform in composition throughout the massof the article being cast and to the discovery of novel combinations ofcomponents that will yield castingsof certain properties or combinationof properties such as strength, ductility, thermal and electricalconductivity, expansion, and the like. a

I have approached the problem of making castings from an entirelydifferent point of view, namely, from the point of view of obtainingcastings containing two or more components in which the relativeproportion of one (or more) of the components is a maximum at onesurface of the casting and becomes progressively lower toward theopposite surface and the relative proportion of one (ormore) of theother components is at a maximum at said opposite surface and becomesprogressively lower'toward the surface having the maximum concentrationof the first components.

' The term surface is used generically herein to apply to any of theexterior surfaces of a casting. Thus, for example, the term surface mayapply to the fiat side of a thin strip or to a relatively small surfaceat one extremity of such a strip.

It will readily be appreciated that a casting in the form of a thinstrip of solid material consisting of two or more components in whichthe concentration of one (or more) of the components is at a maximum atone extremity of the strip and the concentration of one or more'other ofthe components is at a maximum at the other end of the strip and theconcentrations of said components decrease progressively toward andbeyond the center of the strip will have great utility for a variety ofpurposes, e. g., the determination of the best proportion of theingredients for a particular purpose. Thus, for example, a casting, inthe form of a thin strip, of magnesium and aluminum in which theconcentration of magnesium is at or near 100% at one end, theconcentration of aluminum is at or near 100% at the other end and therespective relative proportions decrease progressively toward and beyondthe center will be a valuable research tool since it is possible to testthe properties of any desired portion of the strip and thus arrive atthe optimum relative proportions for a particular purpose withoutnecessity of making an excessively large number of individual andhomogeneous castings in which the proportions vary from 100:0 to 0:100.

The method of the invention is also of utility in casting objects havingother properties in gradually increasing degree such as, for example,optical density, electrical resistance, and the like. Thus, for example,if a dye and a wax are two components cast by the method ofthe 2,837,77TPatented June 10, 1958 'ice invention, a wax casting will be obtainedhaving a maximum concentration of dye at one surface and a minimumconcentration of dye at the other. Similarly, materials of differentelectrical resistance characteristics may be cast in such a manner thatthe casting will have excellent electrical. conductivity at one surfaceand high electrical resistance at the opposite surface.

it will also be appreciated that a casting, in the form of a thin strip,wherein the relative proportion of one of the components is at a maximumon one side, the relative proportion of the other component is at amaximum on the other side and the relative proportions of the componentsdecrease progressively toward and beyond the center will also have greatutility. Thus, for example, if such stripsare composed of metalcomponents they will have superior thermal conductivity while presentingone type of metal at one face and a different metal at another face.Such strips would have particular utility as bi-metallic thermostatelements and would be of advantage in such use by reason of the factthat the shearing stress, which in bi-metallic elements made of twometal strips of different materials joined together is inherentlyconcentrated at the plane of junction, is distributed throughout theelement and would hence possess superio sensitivity and accuracy.

, In accordance with my invention, material containing at least twocomponents, mixtures of which are solid in the temperature range withinwhich they are to be used or tested and in which the relative proportionof one (or more) of the components'is at a maximum at one surface andbecomes progressively lower toward the opposite surface, and therelative proportion of one (or more) of the other components is at amaximum-at said opposite surface and becomes progressively lower towardsaid one surface, is cast by confining the components, in a liquidstate, in a chamber defined by closely and substantially equidistantlyspaced walls of heat conductive, inert material, maintaining one of thewalls at a relatively high temperature below the boiling point of thelowest boiling component and maintaining the other of said walls at arelatively low temperature above the melting or freezing point of thecomponent having the highest melting or freezing point until therelative pro portions of the components vary in different portions ofthe chamber or reach a state of equilibrium in a given portion of thechamber. When the desired variation in relative proportions, or a stateof equilibrium has been reached, both walls are cooled to a temperaturebelow the eutectic temperature of the components to solidify the liquid.i a

The method of the present invention is applicable to the casting ofliquifiable or normally liquid components one or more of which may bemetal, e. g., mercury, gallium, Woods metal, magnesium, aluminum,copper, lead, iron, and the like, or thermoplastic material, e. g.,waxes, resins, and the like, provided that all proportions of thecomponents in the casting are solid in the temperature range withinwhich the casting is to be used or tested.

The term eutectic temperature, as used herein applies not only to thelowest constant melting point of any mixture of the constituents of ametal alloy, but also to the lowest constant melting point of anymixture of other components, e. g., organic components, of the mixturebeing cast.

While the invention is not to be limited by any theory expressed herein,it is believed that the novel results obtained by the method of thepresent invention are due to thermal diffusive forces applied to themolecules of the components in the liquid or liquified mixture in that-3 subjected toetemperature gradient -It has been observed that thedegree to which different molecules tend to accumulate at the lower andhigher ends, respectively, -of the temperaturegradieut depends upo'n themagnitude of t-he temperature gradient which is defined as -thedifferen'ce l in i temperature per :unit 'of distance. -Inasmuch as thedilference between the higherand #lower': temperatures to" which amixture: of components to be subjected is -limited by the boiling pointof the lowest boiling component and the melting or freezing pointof t-hehiglr est-melting componeng'itis desirable, in order to achieve a'hightemperature gradient, to make thedistance across whic-h the temperaturegradient is effecttive, i. e., from onewall of the'chamber-to theother-,as small as possible. Thus, while the distance between the wallsand consequentlythe thickness of'the casting is not particularlycritical, it is preferred that the Wall spacing in the chantber-in whichthe casting isetfected be of'the order of a fraction of an inch,preferably as small as about 0.01

to about 0.15 inch.

It'has also been observed, that thermal diffusion forces actsurprisingly rapidly in bringing about an accumulation of certainmolecules or atoms'adjacent'one wall and of other molecules'or atomsadjacent-the opposite wall. concentration of the components at oppositesurfaces-of. the castingare'notdesired, it is-within the scope of theinvention to solidify the liquid mixture withimthe chamber shortly aftera-temperature gradient has been effectively imposed upon it.

When it is desiredto cast a flat strip, the chamber in which'the castingis effectedmay be operated in a vertical or horizontal positiondepending upon whether a gradationof the relative proportions of thecomponents is desired from side to side or from end to end. If thechamber is operated in the vertical position, the molecules accumulatingadjacent the relatively hotter wall will ascend by thermal convectiontoward the upper end of chamber and the molecules accumulating adjacentthe relatively cooler wall will descend, likewise by thermal convection,to the'lower portion of the chamber. Thus, after equilibrium conditionshave been obtained and both walls have subsequently been cooled,preferably with rapidity, to solidify the material in the chamber, acasting will be produced which, at one end, consists exclusively orcontains a maximum concentration of one of the components and at theother end consists exclusively or contains a maximum'concentration ofanother component. When the thermal 'difiusion separation chamber isoperatedvertically, as described, it may be formed by two'closelyi'spacedflat"plates, by'the inner surface of an outer tubeandthe' outer surface of an inner concentric tube or by any otherdesiredconfiguration of substantially equi- "distantly: spaced walls.

If it 'is"desir'ed to cast'a strip wherein the relative proportions oftheco'mpo'nents varyfrom side to side, the chamber is operated in thehorizontal position, the wall that is heated to the relatively highertemperatures preferably being on top. In-this embodiment of the method,thermal circulation of the components-within the chamber issubstantially absent, the molecules of one of the components-againaccumulating adjacent the relatively highly heated wall and themolecules of another component accumulating adjacent the lesshighlyheatedwall. When a state of equilibrium has been obtained the walls are,as in'the vertical embodiment of the method, cooled, preferably withrapidity, to solidify the mixture.

, The advantages and utility of the method and product 'of thepresentinvention wi l become further apparent from the following descriptionmade with reference to the accompanying drawing wherein:

Figure 1 is -a cross-sectional view in elevation of a chamber inaccordance with one embodiment offthe invention;

For thisreason, where maximum differences in melting point.

.Figure2 istaschematic view of a casting formed in the mannerillustrated in Figure 1;

Figure 3 is a cross-sectional view in elevation of apparatus similar tothat shown in Figure 1 wherein the chamber used is in a horizontalposition; and

Figure 4 illustrates schematically an embodiment in which castings inshapes'other than fiat strips, e. g., tubes or cylinders, mayirbelformed.

Referring now toFigure 1, thechamber 10 for forming a casting suchas'thatshown at "11 in Figure 2,is defined by closely and substantiallyequidistantly spacedwalls 12 and 14 provided with means, such as coils16 embedded therein, for'maintaining the'walls at different preselectedtemperatures. The ends of the chamber 10 are sealed by any suitablemeans such as a ga'sket17 and preferably two conduits 19 and 20communicating with the exterior of the apparatus are provided, one forintroducing the mixt-ure of components to be passed into the' chamber 10and the'otherforwenting the chamber. I

In accordancewith one preferred embodiment of the -method' of theinvention,-twoor more components in liquid orliqu'ifiedform,-e. g., 50parts lead and SO-parts 327.4 C.-and'232 C., respectively. One of thewalls 12' and 14 is maintained-at a temperature above about 327 C., themelting point of the component having the highest The other ofthe-wallsis maintainedat a higher temperature but below 1620 '-C., theboiling point of thelowestboiling component. --After the relativeproportions of the components in a given portion of the chamber -10 havereached a state of equilibrium, the walls Hand 14 are rapidly cooled toa temperature below the eutectic-point,e. g., below about C., andpreferably to room temperature, to solidify the liquid.

The casting thus obtained, shown schematically in Figure 2, will consistpredominantly of tin, indicated'by .ts in Figure 2, at one end and oflead, indicated by'small circles at the otherend, the relativeproportions oflead and tin decreasing towards and beyond themid-point'of the strip, as indicated in Figure 2.

The embodiment illustrated in Figure 3 is substantially similar to thatshown in Figure 1 except that the chamber 10a is horizontal, the walls12a'a'nd 14a are likewise horizontal,-and the conduits 19a and 20acommunicate with the opposite ends of the chamber. A stripcast in achamber of this type has a gradation of concentration from side to side,as indicated by the'small xs and circles shown in the chamber 10a.Strips so made of two metals would be of'great utility as'bimetallicthermostat elements.

The embodiment illustrated in Figure 4 comprises two concentric tubes 21and 22 forming an annular'chamber 24. The tubes'are maintained out ofcontact with another by means of ring shaped gaskets such as gasket 26.The temperature of the inner tube 21 is controlled by any suitable meanssuch as a coil of resistance wire 27 and the temperature of the outertube 22 may likewise be controlled by any'suitable means such as a coilof resistance wire 29. Conduits 30 and 31 communicating with the chamber24 areprovided for introducing the components to be cast and venting thechamber.

In operation, the, procedure is substantially the same as described inreferenceto Figure 1, it being preferable that the inner and outer tubes21 and 22 be constructed of a material havingrespectively higher andlower thermal expansion coefficients than the thermal expansioncoeflicients of the components being cast so that the cast tube may beremoved from the chamber with a minimum of damage to the tubes 21 and22.

It is to be expected that various modifications will readily occur tothose skilled in the art upon-reading this description. All suchmodifications are intended to be included within the scope 'of theinvention-as defined'in the accompanying claims.

I claim:

1. A method of casting solid material containing at least two componentsthat are non-reactive and miscible with one another in the liquid statewhich comprises confining the components, in a liquid state, in achamber defined by closely and substantially equidistantly spaced wallsof heat conductive, inert material, maintaining one of the walls at ahigher temperature below the boiling point of the lowest boilingcomponent and maintaining the other of said walls at a lower temperatureabove the solidification temperature of the highest melting componentuntil there is a variation in the concentrations of the components indilferent portions of the chamber, and then quickly cooling both wallsto a temperature below the eutectic temperature to solidify the liquid.

2. The method defined in claim 1 in which the chamber is in a verticalposition.

3. The method defined in claim 1 wherein the chamber is in a horizontalposition.

4. The method definedin claim 1 wherein the walls defining the chamberare flat.

5. The method defined in claim 1 wherein the chamber has an annularshape defined by the walls of vertical concentric tubes.

References Cited in the file of this patent UNITED STATES PATENTS1,882,917 Ripley Oct. 18, 1932 1,994,634 Broughton Mar. 19, 19352,058,621 Pile Oct. 27, 1936 2,094,482 Weder Sept. 28, 1937 2,106,590Boegehold et al. Jan. 25, 1938 2,214,976 Stockkarger Sept. 17, 19402,234,904 Pile Mar. 11, 1941 2,326,531 Gates Aug. 10, 1943 2,386,112Harkins Oct. 2, 1945 2,401,075 Humes May 28, 1946 2,431,474 Gaudenzi etal Nov. 25, 1947 2,527,387 Arndt Oct. 24, 1950 2,583,008 Olsen Jan. 22,1952 2,602,763 Scafi et al. July 8, 1952 2,615,060 Marinace et al. Oct.21, 1952 OTHER REFERENCES Transactions of the Amr. Inst. of Mining andMetallurgical Engineers (Iron and Steel Div.), vol. 135, pub. 1939.Article by Hayes and Chipman. Entire article, pp. 85-132. Pp. 123 and124 relied on.

Journal of Metals, vol. 4, 1952, pp. 747-753 and pp. 861-865. Articlesby Pfarm.

